It sounds almost like vacuum tubes if you're old enough to remember those. The sound changes pitch whenever I use the scrool wheel on my mouse. At first I thought it was a fan but I turned them all off including CPU fan and the noise is still there. It seems to be in the area of the DIMM slots. Its an Aopen KK77-600N.

Try moving the audio-card as far away from the AGP-card as possible.

What's it whistling?

"Zippa-dee-doo-da! Zippa-dee-day! My oh my! What a wonderful day!!!"

Sorry, I know that's not helping. I just could not resist it. I am sure you are finding this distressing, all I can say is it really must be electrical interference from some source that's powerful enough to make it pick it up.

Or, it may be just broken, and it will always do this.

Here's someone else with your problem on another site:

http://www.webhostingtalk.com/archive/thread/125707-1.html

Could you return it?

Problem solved. After literally putting my head in the computer case I found its the power supply thats whistling. Did a search and it seems to be a common problem with this Enermax model. Its a bad capacitor. Its only 2 months old and was expensive.

Thats sad! Cuz Enermax is a good brand too!

Two months old "should" be under warranty though. Doesn't hurt to check.

Im sending it back today. I think Im going to ask if they will exchange it for an Antec. I put my old Antec in and no whistling and my CPU temp dropped almost 10*F. Id like to keep using that one but its 4 years old and only 300w.

When a motherboard starts to beep for overheating is that due to the cpu fan or just the cpu in general?

It could be the CPU fan failing and letting the CPU run hot or the temp warning setting in the BIOS is set too low. Theres a program called HOT CPU that tells what your system temps are.
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